Facts about the animal kingdom

Are There Animals That Don't Feel Pain?

María Luz Thurman
By María Luz Thurman, Biologist/ornithologist. October 2, 2023
Are There Animals That Don't Feel Pain?

The concept of pain in the animal kingdom has been the subject of zoological debate and study for the ages. The question of whether there are animals that do not feel pain raises fundamental questions not only about biological study, but about ethics. Specifically, it asks questions about human treatment of the animals with which we share this planet. As this scientific study advances and our knowledge deepens, a more nuanced picture of how different species experience and respond to pain emerges.

In this AnimalWised article, we discuss pain perception in the animal kingdom by asking are there animals that don't feel pain? We examine both the similarities and differences in pain responses between various species to answer this question. We also examine some of the ethical considerations the topic of pain response in animals raises.

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  1. Are there animals that don't feel pain?
  2. Why are there animals that do not feel pain?
  3. Does it matter if animals feel pain?

Are there animals that don't feel pain?

As stated above, the concept of animals that do not feel pain is the subject of study and debate in the scientific community. It is generally believed that most animals have the ability to experience some form of pain sensation. The reason for this is that it provides them an important evolutionary advantage. Pain allows them to learn so they can avoid physical harm and dangers in their environment.

To understand whether an animal feels pain, we need to consider the concept of pain more closely. Pain is feeling of distress that is both a sensory and an emotional experience. Since we humans know ourselves to be emotional beings and can report on our physical sensation, we know that we experience pain. However physically adaptive they may be, we broadly consider animals to be less emotionally complex than humans.

For this reason, we can say that pain perception and response vary considerably between animal species. Some animals have a very underdeveloped nervous system compared to more complex animals such as mammals. This may make their experience of pain less intense or it may mean they don't even experience pain as we know it. This provokes the following question:

Do animals feel pain or is it simply a reflex action?

We can see that some animals will experience something which would be traumatically painful to us and carry on as if nothing happened. For example, a brown crab (Cancer pagurus) will tear their own arm off if they feel threatened or need escape from a situation where they feel trapped. The crab does not seem to show evident signs of pain and will continue on.

Some studies contest whether the crab does not feel a sensation. One study shows that a brown crab will experience a rapid elevation of glucose and lactate levels after an arm is removed[1]. This suggests that the crab might experience a sensation equivalent to pain, but this has not been proved. Other theories suggest these elevations simply facilitate the escape response.

One of the key factors in whether animals experience pain is due to the differentiation between types of vertebrate and invertebrate animals. Humans are vertebrate animals and have a more complex central nervous system than invertebrates. In vertebrates make up almost 98% of the world's animal species, but they don't have nerves like we do.

Some animals do not have a centralized brain such as bivalve mollusks. Despite this lack of a brain, they do respond to harmful stimuli by closing shut. This helps protect their fleshy parts with their hard shell. The nature of this response is not fully understood.

It is important to note that the pain response is not limited to mammals, as is often thought. Many animals other animals have nervous systems that allow them to detect and respond to painful stimuli. Even some simpler organisms such as jellyfish have been shown to have responses to noxious stimuli. While they may be less complex, there are very few animals which do not have a central nervous system at all.

If we want to know whether there are animals that do not feel pain, the answer is that we do not know. We do know that different animals will experience pain very differently, but the extent to which each animal does or does not feel pain is unknown.

Why are there animals that do not feel pain?

Although it has not been conclusively proven that there are animals that do not feel pain, the experience and response to pain varies widely among different species. Understanding how different animals perceive pain has important implications for our relationship with other life forms on the planet. It is important to understand why some species may appear less sensitive to pain or may show different responses to painful stimuli.

Animals have very diverse nervous systems in terms of complexity and structure. Species with less developed nervous systems include invertebrates. They may have less obvious or less intense pain responses than animals with more complex nervous systems. However, even within these types of animals there is a a great diversity in terms of sensory organs, tissues and receptors.

For example, there are many invertebrates which have nociceptors. These have been found in aquatic invertebrates such as the sea slug (genus Aplysia). Some studies claim that the nociceptors which sea slugs and some bony fish have are similar to those of mammals[2]. While this suggests they can feel pain in the same way as mammals, many lack a centralized brain which implies the converse.

It is also possible that pain responses may be less visible or obvious to human observers. This may be due to differences in the anatomy or behavior of the species. Some animals may have a high pain tolerance without showing obvious signs of discomfort. In evolution, animals have developed a wide range of strategies to survive. These strategies can influence how they perceive and respond to pain. Some animals may prioritize other forms of survival, such as reproduction or foraging, over responses to pain.

Furthermore, the understanding of pain in animals is often based on limited observations and experiments. The lack of research in some species may lead to an incomplete understanding of their abilities to feel pain, but we must understand that variation in pain perception and response across the animal kingdom is a consequence of evolutionary and adaptive diversity.

Each species has developed its own set of strategies and mechanisms to deal with harmful stimuli based on its evolutionary history and environment. It is important that research continues to explore these aspects to better understand the experience of pain across all walks of life.

Are There Animals That Don't Feel Pain? - Why are there animals that do not feel pain?

Does it matter if animals feel pain?

The claim that there are animals that do not feel pain is a controversial topic and not supported by solid scientific evidence. It is often thought that animals such as fish, snails or butterflies do not feel pain. We cannot confirm that there are animals that do not feel pain, but it is likely they do not feel it in the same way we do. They have nervous systems and pain receptors that allow them to detect and respond to harmful stimuli. Pain perception is an important characteristic that has evolved in many species for their own survival and well-being.

We must remember that our understanding of how different animals perceive pain remains an active field of study in biology and ethology. Research continues to shed light on animals' abilities to sense and respond to pain. It is generally recognized that most species have the capacity to experience some level of discomfort in response to harmful stimuli.

Why it matters whether an animal feels pain is due to the ethical considerations it raises. Recognizing that animals feel pain presents questions about how we treat animals. For example, some dog guardians still think that it is OK to strike their dog when they misbehave. Even if the dog does not show signs of pain, it doesn't mean it doesn't affect their physical and emotional wellbeing.

Another example is the aforementioned crab. There are crab fishermen who will catch live crabs and remove one of their claws before returning them to the water. Since crabs are able to regenerate their lost limb, many think of this as a way to harvest a catch of food without having to kill the animal. However, the question of whether they feel pain may suggest this practice is unnecessarily cruel, among other issues it raises.

Share your thoughts over whether there are animals that feel pain and the ethical questions this topic raises by sharing in the comments.

If you want to read similar articles to Are There Animals That Don't Feel Pain?, we recommend you visit our Facts about the animal kingdom category.


1. Elwood R. W. (2021). Potential Pain in Fish and Decapods: Similar Experimental Approaches and Similar Results. Frontiers in veterinary science, 8, 631151.

2. Sneddon L. U. (2015). Pain in aquatic animals. The Journal of experimental biology, 218(Pt 7), 967–976. https://doi.org/10.1242/jeb.088823

  • Braithwaite, V. (2010). Do fish feel pain?. OUP Oxford.

  • Harrison, P. (1991). Do animals feel pain? Philosophy, 66(255), 25-40.

  • Jensen, T.S., & Gebhart, G.F. (2008). New pain terminology: a work in progress. Pain, 140(3), 399-400.

  • Miller, C. (2021). Do animals feel pain in a morally relevant sense? Philosophia, 49(1), 373-392.

  • Morton, D.B., & Griffiths, P.H. (1985). Guidelines on the recognition of pain, distress and discomfort in experimental animals and a hypothesis for assessment. Vet Rec, 116(16), 431-6.
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Are There Animals That Don't Feel Pain?